Assertion (A): The walls of bacterial cells are treated with lysozyme to release the genetic material (DNA). Reason (R): Plant cells require treatment with cellulase, and fungal cells require chitinase to break down their respective cell wall structures for DNA isolation.
A is True: Lysozyme is used for bacterial cells. R is True: Cellulase is for plants, chitinase for fungi. R supports A by providing related factual examples, but does not explain *why* lysozyme works on bacteria (A).
Question 492 of 535
📘 CLASS XII
Assertion (A): Ligation of foreign DNA at the $Pst$ I site of pBR322 causes insertional inactivation, leading to the loss of tetracycline resistance. Reason (R): The general principle of insertional inactivation is that the foreign DNA is inserted within the coding sequence of an antibiotic resistance gene, making it non-functional.
A is False: $Pst$ I is located within the ampicillin resistance gene ($amp^R$) [31, Figure 9.4]. Insertion here causes loss of ampicillin resistance, not tetracycline resistance. R is True: R correctly describes the mechanism of insertional inactivation.
Question 493 of 535
📘 CLASS XII
Assertion (A): Ever since the seventeenth century, the whole approach to understanding natural phenomena became anthropocentric. Reason (R): The focus of human knowledge, particularly in physics and chemistry, was directed toward developing technologies that add to the comfort and welfare of human lives.
A is True: The approach became anthropocentric (human-centered). R is True: The output of physics and chemistry (engineering, technologies) worked specifically for human comfort and welfare. R explains why the approach became anthropocentric.
Question 494 of 535
📘 CLASS XII
Assertion (A): Asexual reproduction preserves genetic information efficiently. Reason (R): Sexual reproduction provides opportunities for variation and the formulation of unique combinations of genetic setups, some of which may be beneficial.
A is True: Asexual reproduction preserves genetic information. R is True: Sexual reproduction allows for variation. Both statements are facts about modes of reproduction, but R does not explain why Asexual reproduction preserves genetics.
Question 495 of 535
📘 CLASS XII
Assertion (A): The first artificial recombinant DNA was constructed in vitro by linking an antibiotic resistance gene with a native plasmid of Salmonella typhimurium. Reason (R): This linking process was achieved by the enzyme DNA ligase, which acts on cut DNA molecules and joins their ends.
A is True: The first recombinant DNA construction involved linking an antibiotic resistance gene with a S. typhimurium plasmid. R is True: DNA ligase was the enzyme used to link the cut DNA pieces. R details the necessary mechanism required to achieve A.
Question 496 of 535
📘 CLASS XII
Assertion (A): Maintenance of the introduced DNA in the host and its transfer to the progeny is the final basic step in genetically modifying an organism. Reason (R): The first basic step in genetic modification is the identification of DNA with desirable genes.
A is True: Maintenance/transfer is the third step. R is True: Identification is the first step. Both are true steps, but R does not explain the necessity or mechanism of A.
Question 497 of 535
📘 CLASS XII
Assertion (A): The enzyme that cuts DNA, known as restriction endonuclease, was isolated in 1963. Reason (R): This restriction enzyme was one of two enzymes responsible for restricting the growth of bacteriophage in Escherichia coli.
A is True: Restriction endonuclease was isolated in 1963. R is True: The enzyme was isolated because of its role in restricting bacteriophage growth. R provides the context for the discovery mentioned in A.
Question 498 of 535
📘 CLASS XII
Assertion (A): The first restriction endonuclease, Hind II, was found to always cut DNA molecules at a particular point by recognising a specific sequence of six base pairs. Reason (R): The recognition sequence of Hind II is a specific DNA nucleotide sequence on which its functioning depends.
A is True: Hind II recognizes a specific six base pair sequence. R is True: The functioning of Hind II depended on recognizing this specific nucleotide sequence. R establishes the principle that makes A possible.
Question 499 of 535
📘 CLASS XII
Assertion (A): In the restriction enzyme name $EcoRI$, the Roman number 'I' indicates the order in which the enzyme was isolated from that strain of bacteria. Reason (R): The letter 'R' in $EcoRI$ is derived from the genus of the prokaryotic cell from which it was isolated.
A is True: Roman numerals indicate the order of isolation. R is False: 'R' is derived from the strain name (RY 13). The first letter (E) is derived from the genus.
Question 500 of 535
📘 CLASS XII
Assertion (A): Exonucleases remove nucleotides from the ends of the DNA strand. Reason (R): Endonucleases make cuts at specific positions within the DNA.
A is True: Exonucleases remove nucleotides from the ends. R is True: Endonucleases cut internally at specific positions. Both statements are correct definitions, but R does not explain the function of A.
